Display devices are ubiquitous. There are many situations where viewers of apparatuses including display devices are concerned about privacy issues when using the display device in public or unsecure environments, for example when working on confidential or sensitive documents. Examples of display devices where such concerns exist include computer apparatuses, such as desktop computers, laptop computers and tablets; mobile communication devices, such as smartphones; and display devices in static installations, such as kiosks and ATMs. In such circumstances, the primary viewer is required to be vigilant of other people in their surroundings and to take action to obscure or turn off the display device when unwanted, secondary viewers are present. It would be desirable for the display device to have a privacy control function which assists the primary user in preventing unwanted viewing of the displayed image.
There exist privacy functions which may determine that secondary viewers are viewing a display device, and in response may blur the displayed image. However, typically the display device is then blurred for everyone, including the primary viewer. This is less than desirable and it may be more constructive for the primary viewer to be able to continue viewing.
Display devices which are directional are known. Examples of a type of directional display device using a directional backlight are disclosed in U.S. Patent Publ. No. 2012/0127573, and U.S. Patent Publ. No. 2014/0240828. Directional display devices of this and other types may direct the displayed image into a viewing window, which may have a finite width in a viewing plane, being typically much narrower than the viewing width of a conventional display device. Such a directional display device may be operated in a mode in which the displayed image is directed into a viewing window of relatively narrow width in order to provide a privacy function. The privacy function may be used to provide the displayed image with reduced or negligible visibility to a secondary viewer.
An aspect of the present disclosure is concerned with the functionality of a directional display device used to provide a privacy function.